The present application generally relates to the field of rotary thermoforming apparatus and methods of using same. More particularly, the present application relates to an improved rotary thermoforming apparatus that allows for continuous high speed part production.
Thermoforming has been used to mass produce plastic parts including packaging for food products. A sheet of thermoplastic material or other plastic material is positioned over one or more mold cavities. In some instances a vacuum is used to draw the thermoplastic or plastic into the mold cavities, and in other instances a positive pressure may be used to force the thermoplastic or plastic material into the mold cavities.
Furthermore, rotary thermoforming of parts has also been used where an extruded sheet of thermoplastic or plastic material is fed over the surface of a rotatory drum which contains a series of mold cavities on the outer surface of the drum. The material within each of the mold cavity cools as the drum rotates and is eventually removed from the mold cavity as a formed part, where it may undergo further processing steps in some instances.
In some applications one or more plug assist members may be used wherein the plug assist member is inserted into a corresponding female mold cavity forcing the thermoplastic or plastic material against the mold cavity. Typically, the rotary drum carries a plurality of cavity flats about the outer surface of the drum. A plug assist assembly containing plug assist members corresponding to the female mold cavities in a cavity flat is positioned over or above the drum, but does not rotate with the drum. When a cavity flat rotates into position beneath the plug assist assembly, the plug assist members are pushed into the mold cavities thereby forcing the thermoplastic or plastic material against the mold cavity. Some designs, such as U.S. Pat. No. 4,421,712 does follow the drum, but does not rotate with the drum. After a moment, the plug assist members are withdrawn and the rotary drum is further rotated until the next cavity flat is positioned beneath the plug assist assembly, and the plug assist members are again moved into the female mold cavities to force the thermoplastic or plastic material against the mold cavity. After a moment, the plug assists are withdrawn and the rotary drum is further rotated until the next cavity flat is positioned beneath the plug assist assembly, and process is repeated as each adjacent cavity flat is moved into position beneath the plug assist assembly.
A drawback of using plug assist members positioned above the drum in forming the parts is that, in some cases, the rotary drum may not continue to rotate while the plug assist members are moved into and out of the mold cavities on each of the respective cavity flats. As a result, the process of forming parts on a rotary drum with a plug assist assembly positioned over or above the drum may be limited in terms of the speed of operation because of the time it takes for the plug assist members to enter and exit the mold cavities for each of the respective cavity flats on the surface of the rotary drum.
Accordingly, it would be desirable to provide a rotary thermoforming apparatus and method of using the same, wherein parts could be continuously formed without requiring the rotary drum to stop as the plug assist members are inserted into and withdrawn from the cavities for each of the respective cavity flats on the outer surface of the rotary drum as the drum rotates, and also desirable to provide a rotary thermoforming apparatus and method of using the same where the parts could be formed and the rotary drum rotated at a faster rate of speed, to increase overall production, reduce cost, and provide for increased efficiency.